Thermo Fisher Scientific CyberScan DO 300 - Manual (Page 52)

Instruction Manual DO 300
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14 DISSOLVED OXYGEN & METER THEORY
Dissolved Oxygen (DO) refers to the volume of oxygen that is contained in water. There are
two main sources of DO in water: from atmosphere and photosynthesis. Waves and tumbling
water mix air into the water where oxygen readily dissolves until saturation occurs. Oxygen is
also produced by aquatic plants and algae as a by-product of photosynthesis.
The amount of DO that can be held by water depends on 3 factors: water temperature, salinity,
and atmospheric pressure.
1. Amount of DO increases with decreasing temperature (colder water holds more oxygen).
2. Amount of DO increases with decreasing salinity (freshwater holds more oxygen than
saltwater does).
3. Amount of DO decreases with decreasing atmospheric pressure (amount of DO
absorbed in water decreases as altitude increases).
The chart below shows the solubility of DO in mg/L in water at various temperatures.
Solubility of oxygen in water contact with water saturated air at
standard atmospheric pressure
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60
Temperature °C
S
o
lubilit
y
mg/L
Figure 38: DO Solubility in Water vs Temperature °C